In U.S. Pat. No. 3,481,945, tetrabenzimidazole, tetrabenzothiazole and tetrabenzoxazole were described and claimed. A single example of a method of producing the compound was detailed. In that method, 2,3-diaminobenzoic acid was refluxed with meta-cresol and a copper compound to form a dark substance having a melting point above 400.degree. C. The substance was described as copper tetrabenzimidazole, a chelate. The properties of the isolated compound were described in depth; an acidic solution was strongly colored, and both acidic and neutral solutions exhibited strong fluorescence when excited by visible light.
However, it was recently determined that the substance produced by following the method disclosed in the patent was not copper tetrabenzimidazole, but rather the well known compound fluorindine (5,12-dihydroquinoxalo[2,3-b]phenazine). The error was discovered when mass spectrometry work on the isolated substance indicated that the substance had the empirical formula of fluorindine. A sample of fluorindine was then prepared by an established synthetic process; that sample had properties identical to those of the compound isolated by the method disclosed in the patent. Thus, the substance isolated and described in the patent is fluorindine, not copper tetrabenzimidazole.